Write Best-Effort / Napkin Math approximation of Min. Cost of Known Attack metric for several attacks.

[nathan-at-least]

Suggested Improvement

We can do a "napkin math" Min. Cost of Known Attack for a few known attacks.

For "napkin-math" style metrics, we can use these data sources / extrapolations:

• historical Zcash mining revenue to provide PoW attack cost estimates.
• estimate size of ZEC stake based on a model that assumes greedy staking participants, 0 volatility, and 0 cost for staking/unstaking and/or exchange. We then assume participants seek to maximize yield against a "global average yield" value. From all of those assumptions, we can work backwards to determine how much ZEC would be staked for a given amount of block rewards to stakers.

The second bullet here requires a fair amount of documentation, deserving its own ticket. (I have done this napkin math in the past in personal notes.)

I hope it's obvious that the approach is extremely speculative relying on many unrealistic assumptions and projections, so we cannot treat the results as anything other than a "smoke-test". What I mean is that if the result says "the min cost of this attack is estimated at $10" that would be concerning. If it is $10,000,000 dollars, however, we shouldn't place a lot of confidence on that number as a security metric, and instead conclude simply "this approach may be feasible".

[nathan-at-least]

BTW- this kind of projection and analysis was performed for Ethereum prior to their transition. One high-quality example is Ethereum 2.0 Economic Review: An Analysis of Ethereum’s Proof of Stake Incentive Model, by Tanner Hoban and Thomas Borgers. We're very unlikely to achieve that level of rigor or thoroughness here.

[nathan-at-least]

More on the "predicted amount of ZEC" model: the more sophisticated that model gets, the more it gets into the messy world of macro-economics-like analysis, IIUC.

For example, if we replace the "general yield rate" with specific known alternative yield rates, such as other PoS of Defi Systems then assume some of them adjust their rates or issuance schedules dynamically in response to competition, it starts to get really complex. However, this seems like a crucial area for general cross-ecosystem PoS security (and ultimately bleeds into stuff like central banking policy). Weird trajectory.

One step in this direction is Competitive equilibria between staking and on-chain lending, by Tarun Chitra.